[SRU][J][PATCH 1/1] UBUNTU: SAUCE: Revert "btrfs: avoid unnecessary device path update for the same device"

[Matthew Ruffell]

BugLink: https://bugs.launchpad.net/bugs/2107516

This reverts commit fc83c00ca63bc3a29778957170ccb96fabccf44c (ubuntu-jammy).

"btrfs: avoid unnecessary device path update for the same device" introduced
a regression in the jammy kernel that manifests in two ways.

1) When mounting a btrfs LVM volume, the path changes from

/dev/mapper/VG0-LV0
to
/dev/VG0/LV0

which breaks existing applications that expect a /dev/mapper file.

2) Running lsblk with duplicated mountpoints no longer list all mountpoints
and instead only prints the first one, e.g.:

sdb            8:16   0   9,1T  0 disk
└─sdb1         8:17   0   9,1T  0 part
  └─hdd2     254:6    0   9,1T  0 crypt /mnt/hdd2
                                        /var/cache/distfiles
                                        /var/cache/binpkgs

becomes

sdb            8:16   0   9,1T  0 disk
└─sdb1         8:17   0   9,1T  0 part
  └─hdd2     254:6    0   9,1T  0 crypt /mnt/hdd2

The author of the patch helped debug the issue in [1] and came to the
conclusion that this patch requires the new btrfs fsconfig mount API
that was introduced in 6.8 and onward.

[1] https://bugs.gentoo.org/947126

Hence, we need to revert this patch for jammy.

Signed-off-by: Matthew Ruffell <matthew.ruffell at canonical.com>
---
 fs/btrfs/volumes.c | 38 +-------------------------------------
 1 file changed, 1 insertion(+), 37 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c0fcac0a1b8e..b5e2daf538d4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -717,42 +717,6 @@ u8 *btrfs_sb_fsid_ptr(struct btrfs_super_block *sb)
 	return has_metadata_uuid ? sb->metadata_uuid : sb->fsid;
 }
 
-static bool is_same_device(struct btrfs_device *device, const char *new_path)
-{
-	struct path old = { .mnt = NULL, .dentry = NULL };
-	struct path new = { .mnt = NULL, .dentry = NULL };
-	char *old_path = NULL;
-	bool is_same = false;
-	int ret;
-
-	if (!device->name)
-		goto out;
-
-	old_path = kzalloc(PATH_MAX, GFP_NOFS);
-	if (!old_path)
-		goto out;
-
-	rcu_read_lock();
-	ret = strscpy(old_path, rcu_str_deref(device->name), PATH_MAX);
-	rcu_read_unlock();
-	if (ret < 0)
-		goto out;
-
-	ret = kern_path(old_path, LOOKUP_FOLLOW, &old);
-	if (ret)
-		goto out;
-	ret = kern_path(new_path, LOOKUP_FOLLOW, &new);
-	if (ret)
-		goto out;
-	if (path_equal(&old, &new))
-		is_same = true;
-out:
-	kfree(old_path);
-	path_put(&old);
-	path_put(&new);
-	return is_same;
-}
-
 /*
  * Handle scanned device having its CHANGING_FSID_V2 flag set and the fs_devices
  * being created with a disk that has already completed its fsid change. Such
@@ -958,7 +922,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 				disk_super->fsid, devid, found_transid, path,
 				current->comm, task_pid_nr(current));
 
-	} else if (!device->name || !is_same_device(device, path)) {
+	} else if (!device->name || strcmp(device->name->str, path)) {
 		/*
 		 * When FS is already mounted.
 		 * 1. If you are here and if the device->name is NULL that
-- 
2.45.2